Arbuscular

Arbuscular is an adjective used in biology to describe structures or relationships related to arbuscules, the branched, tree-like hyphal structures formed by arbuscular mycorrhizal fungi within the cortical cells of plant roots. The term is most often encountered in discussions of arbuscular mycorrhizal symbiosis, a widespread form of endomycorrhizal association.

Arbuscular mycorrhizal (AM) fungi belong to the phylum Glomeromycota and form intracellular structures in the roots of a large majority of land plants. This symbiosis is ancient and ecologically significant, enhancing plant nutrient uptake—especially phosphorus and sometimes micronutrients—while receiving carbon compounds from the host plant. AM associations also influence soil structure and plant drought tolerance through extensive hyphal networks and soil-enmeshment.

The arbuscule is the principal site of nutrient exchange between the fungus and the plant. Inside root cortical cells, the arbuscule maximizes surface area for bidirectional transfer of nutrients and carbon, facilitating phosphorus uptake by the plant and providing carbohydrates to the fungus. Arbuscules are dynamic, forming, operating, and degrading as part of the symbiotic lifecycle. Some AM fungi also form storage structures called vesicles in the roots or surrounding soil.

Arbuscular mycorrhizae contrast with ectomycorrhizae, which form outside root cells. The term arbuscular is used to specify the intracellular, arbuscule-bearing relationship characteristic of this common, ancient plant-fungal symbiosis.